1. Technical Field of the Invention
The present invention relates generally to pressure sensors including a sensor chip for sensing pressure. More particularly, the invention relates to a pressure sensor that has an improved arrangement of sensor chip for minimizing the influence of external vibrations on the pressure sensor.
2. Description of the Related Art
Conventionally, pressure sensors, which include a sensor chip for sensing pressure, generally further include a case, a circuit chip, and a protective gel. The case has an inner end surface, on which the sensor and circuit chips are mounted, and an opening through which the protective gel is filled in the case to protect the sensor and circuit chips. Such a pressure sensor is disclosed, for example, in Japanese Patent First Publication No. 2006-23109.
FIG. 6 shows an existing pressure sensor 30, where a sensor chip 10 and a circuit chip 14 are fixed to an inner end surface 15b of a resin-made case 15 by an adhesive 20. A plurality of terminals 16 are disposed on the inner end surface 15b so as to partially protrude out of the case 15. Wire bonding 18 is applied to electrically connect between the sensor and circuit chips 10 and 14 and between the circuit chip 14 and the terminals 16. Further, to alleviate stress induced by temperature change, a glass seat 11 is interposed between the sensor chip 10 and the inner end surface 15b. A protective gel 19 is filled in the case 15 through an opening 15a of the case 15, so as to protect the sensor and circuit chips 10 and 14, the glass seat 11, and the wire bonding 18.
When the above pressure sensor 30 is installed in an environment with a pressure-receiving surface 10a of the sensor chip 10 perpendicular to the direction of external vibrations transmitted from the environment to the pressure sensor 30, the vibrations may cause the pressure-receiving surface 10a to be displaced by the inertia of the protective gel 19. Consequently, even when there is no change in the actual value of a pressure of the environment, the value of the pressure sensed by the pressure sensor 30 may change, thus resulting in a sensing error of the pressure sensor 30.
For example, as shown in FIG. 7, the pressure sensor 30 may be installed in an interior space formed in a door 40 of a vehicle to sense the air pressure change in the interior space caused by a collision against the door 40. In this case, however, since the pressure-receiving surface 10a of the sensor chip 10 is perpendicular to the direction of vibrations caused by opening and closing operation of the door 40, the vibrations may result in a sensing error of the pressure sensor 30.
To avoid the above problem, one may consider installing the pressure sensor 30 in the interior space of the door 40 with the pressure-receiving surface 10a of the sensor chip 10 parallel to the direction of vibrations. However, in this case, since the sensor and circuit chips 10 and 14 would align in the horizontal direction (i.e., the direction of vibrations), the length of the pressure sensor 30 in the horizontal direction would exceed that of the interior space, so that the pressure sensor 30 could not be accommodated in the interior space.